Encapsulation is a concept in Java that involves bundling data and methods that operate on that data within a single unit or class. The data is typically hidden from other classes, and can only be accessed through methods defined within the same class. This provides a way to protect the data and ensure that it is only modified in a controlled and safe manner.

In Java, encapsulation is achieved through the use of access modifiers such as "private", "public", "protected", and "default" (also known as "package-private"). These access modifiers determine which classes and methods can access the data and methods of a class.

Here is an example of encapsulation in Java:

public class Person {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

In this example, the Person class has two private instance variables: "name" and "age". These variables can only be accessed by methods defined within the Person class. The class also has four public methods: "getName()", "setName()", "getAge()", and "setAge()". These methods provide a way to access and modify the private data of the Person class.

By encapsulating the data within the Person class, we can ensure that the data is only modified in a controlled manner. For example, if we want to change the name of a Person object, we can call the "setName()" method, which validates the input and ensures that the name is set correctly. If we were to allow direct access to the "name" variable, we would have no control over how the data is modified.

Encapsulation is a key concept in object-oriented programming, and is used extensively in Java programming. By encapsulating data and methods within a class, we can ensure that the data is protected and that it is only modified in a controlled and safe manner. This helps to improve the robustness and reliability of our code.